Prior antenna tuners use Z-.theta. type discriminators. Z, e.g., 50 ohms, is the ratio of voltage to current on the RF input. Theta is the phase angle between the input voltage and current. The sensed Z and .theta. drive the loading and phasing servos of an impedance matching network, FIG. 1.
An objection to these prior Z-.theta. discriminators is the plurality of sensors which must be coupled to the RF input. For example, some discriminators require a voltage sensor and a current sensor for detecting Z, and a voltage sensor and a current sensor for detecting .theta., a total of four sensors. Another objection is the undesirable harmonic radiation caused by diode RF rectifiers required by these types of discriminators. A further objection is the complexity and high cost of such circuitry.
A need exists for a simple and inexpensive circuit for supplying the loading and phasing control signals in an automatic antenna tuner. There is a need to reduce the number of sensors coupled to the RF input. There is also a need to eliminate harmonic radiation due to diode RF rectifiers. There is still a further need to provide useful loading and phasing control signals in the presence of extreme mismatch conditions at the tuner input, as well as to achieve uniform sensitivity to tuning error across a wide frequency band, such as 2 to 30 MHz. The present invention satisfies these and other needs in a particularly simple and efficient manner.